。
She had never been so proud of herself before.
Literal
She [topic-は] herself [in-に] that-much pride [object-を] held [thing-こと] [topic-は] until-then was-not.
自分にそれほど誇りを持つ ('to hold that much pride in oneself') uses 誇りを持つ ('to take pride'). ~ことはない / ~ことはなかった is the experiential negation pattern: 'has never X / had never X.' それまで ('until then, up to that point') anchors the never-experience to a specific past moment. The sentence marks a moment of unprecedented self-regard — a first-time peak in the speaker's emotional life.